1. Field of the Invention
This invention relates to a composition containing compounds which inhibit the reduction of testosterone to dihydrotestosterone (DHT) in prostate tissue. The composition is used to prevent excessive levels of DHT in prostate tissue, a major contributing cause of benign prostate hyperplasia (BPH).
2. Discussion of Related Art
Benign prostate hyperplasia (BPH) in mammals, particularly human males, is known to result from prolonged accumulation of testosterone in the prostate. The testosterone is converted in prostatic tissue to a more potent metabolite dihydrotestosterone (DHT). DHT stimulates cellular proliferation in the prostatic tissue, causing enlargement of the prostate.
DHT is produced in a mammal by the reduction of testosterone. Testosterone is bound to the enzyme 5.alpha.-reductase through recognition of a specific sequence of amino acids in the reductase, the active site of the enzyme with respect to testosterone. The testosterone is then reduced to DHT. There are two isoforms of 5.alpha.-reductase in mammals, particularly humans. Type 1 of the enzyme is found predominantly in scalp skin, while type 2 is found predominantly in the prostate. See, for example, Rittmaster, "Finasteride", The New England Journal of Medicine, vol. 330, no. 2, pps. 120-125 (1994).
In the prostate, DHT has a "normal" base level in mammals in order to properly stimulate cellular proliferation within the prostate and to undertake other reported physiological roles. When the DHT levels exceed the base level, excessive cellular proliferation begins, accompanied by prostate enlargement.
Finasteride is a 5.alpha.-reductase inhibitor, approved by the FDA, that has been studied extensively in mammalian, including human, subjects with respect to its ability to treat BPH. Finasteride is a steroid exhibiting an ability to reduce the activity of reductase, particularly the type 2 5.alpha.-reductase. If the enzyme activity is reduced, testosterone present in the prostate, particularly excess testosterone, will not be converted to DHT to create excess DHT in the prostatic tissue.
Other studies have determined that Serenoa repens, also known as saw palmetto, which is from berries of the palmetto palm tree, has an antiandrogenic and antiestrogenic activity in prostatic tissue. See, for example, Sultan et al., "Inhibition of Androgen Metabolism and Binding by a Liposterolic Extract of `Serenoa Repens B` in Human Foreskin Fibroblasts", J. Steroid Biochem., vol. 20, no. 1, pps. 515-519 (1984) and DiSilverio et al. "Evidence That Serenoa Repens Extract Displays an Antiestrogenic Activity in Prostatic Tissue of BPH Patients", Eur. Urol., vol. 21, pps. 309-314 (1992).